Dynamics of Tubes in Fluid With Tube-Baffle Interaction

Abstract

Three series of tests are performed to evaluate the effects of tube to tube-support-plate (TSP) clearance on tube dynamic characteristics and instability phenomena for tube arrays in crossflow. Test results show that, for relatively large clearances, tubes may possess “TSP-inactive modes” in which the tubes rattle inside some of the tube-support-plate holes, and that the natural frequencies of TSP-inactive modes are lower than those of “TSP-active modes,” in which the support plates provide “knife-edge”-type support. Tube response characteristics associated with TSP-inactive modes are sensitive to tube-to-TSP clearance, TSP thickness, excitation amplitude, tube alignment, and the fluid inside the clearance. In addition, tube response is intrinsically nonlinear, with the dominance of TSP-inactive or TSP-active modes depending on the magnitudes of different system parameters. In general, such a system is difficult to model; only a full-scale test can provide all the necessary characteristics. A tube array supported by TSPs with relatively large clearances may be subjected to dynamic instability in some of the TSP-inactive modes; tube response characteristics and impact forces on TSPs for a tube row are studied in detail. Tube displacements associated with the instability of a TSP-inactive mode are small; however, impacts of the tube against TSPs may result in significant damage in a relatively short time.

Dreidimensionale numerische Simulation strömungsinduzierter Rohrbündelschwingungen

“…Bei Turbulenzerregung steigen die Amplituden nahezu linear mit der Anströmgeschwindigkeit an, so daß erhöhte Amplituden über Ähnlichkeitsbetrachtungen reduziert werden können. Schäden infolge von Turbulenzerregung bestehen meist in erhöhtem Abrieb an den Lagerstellen im Leitblech [AuY98,Ble79,Ble85,Cha87,Che85,KoP84]. Zur Absicherung ist jedoch die Kenntnis eines Turbulenzspektrums in der betrachteten Konfiguration notwendig [VDI97].…”

A Theory for Fluidelastic Instability of Tube-Support-Plate-Inactive Modes

“…The natural frequency of the n-th mode for a uniform tube in air given in the RMS displacement value at point A is always larger than that at point B. (If the TSP-active model is dominant, the RMS displacemen t value at point B will be larger than that at point A, see [1]. The bilinear method cannot predict the nonlinear response in this region).…”